Went in today to get some stuff for my dad and couldn't find it... the stuff I've seen from Ansdale is all from the 50s or so. Can you get me an actual paper number?

I actually *did* get a new one to try to digest though. #900032, Prediction of Power Output Performance of the Rotary Engine by Gas Exchange Process Simulation, by various people at Mazda. In it they go and come up with a model to predict intake velocity and thus volumetric efficiency based on port timing. The VE numbers are around the 100% range, often a bit over (this is a peripheral port engine). What's interesting though is that they come up with an "optimum" port timing for the thing! Not only that, but they start to explore variable length intake tracts... of the type that appeared on the R26B a few years later.

 

Thanks for taking the time to look for this. Unfortunately, I don't have a paper number, the reference I have only mentions the title and the year (oct 1968). I had a look at Melbourne Uni but couldn't find it. It might not have actually been published in 1968 so I looked through the books up to 1973. Maybe they don't publish all papers. I'm going to contact the sae and ask them about it, maybe then I could at least get a paper number.

 

a thought ...

there is no displacement standard.

piston pumps came well before otto cycle ic engines. they look like an engine, but just have inlet and outlet check valves in the head. pump displacement rating was volume pumped per rev. for piston pumps with cranks, one rev gets fluid in and out, with 2 strokes. displacement was just number of holes x pumped volume per hole, which for piston engines is the same as swept volume method.

i suspect this practice was applied to ic engines when they were invented, thus the method resulted in same size ratings for 2 vs 4 strokes, and the 2 stroke power advantage.

looking at the wankel as a pump, where just 1 exp and contraction is needed to pump a chamber's worth, the pump method 'one rev' rating can be applied. chamber goes thru 2 exp-contr'n events in 3 revs. in one rev, you have 2/3 of the 'up down' event per chamber, so 13B displacement would be 2/3 x 6 x .65 = 2.6L.

this old method would provide consistent ratings for all 4-stroke engines, regardless of cycles needed to complete the total engine cycle. With all 4 strokes, it just doubles the actual air injested per rev. Mr Wankel (rip) was indirectly suggesting this method, but made it confusing with his geometric approach.

 

2.6 period. sure there is no displacement standard, but when you *use* a rotary, you have to use it like any other engine. so the displacement "standard" is based on rpm, since that is all an engine can do, revolve.

trust me guys, i didn't like to hear it at first either, but dave coleman explained it just how it is.

yes each chamber is .65L. yes 1.3L is the displacement of one firing per spark plug, but it's a piston world so unless you think you're going to convince a supra owner he really has a 1.5 liter engine, you might as well accept things as they are pragmatically.

 

This is still getting back to using the output shaft as a point of reference which really is a 'floating' reference because it is simple to design engines that spin the output shaft at different speeds compared to the real engine speed. If I got a piston motor and geared the output shaft different amounts then a different capacity would be measured each time for the same engine. It might sound silly but this is exactly what the rotary is doing.

 

Read this, it explains why I think the output shaft cannot be used to measure displacement.

http://mikesdriveway.com/misc/rotor.doc

 

Side note. Was at the SAE conference in Detroit. Saw a paper various Mazda engineers put on about the Renesis. The displacement question came up, and I hung around to see where it'd go. The guy brought up the 3.9L thing.

... uh... well. Translation problems meant this took far longer to play out than it really should have... they ended up saying it was equivalent to a boinger of twice the displacement. I think.

I really should learn Japanese.

 

Wish I was there Do you have any details about the paper?

 

Paper went over the differences in power and emissions the side exhaust ports made first off. The *power* difference isn't solely because of the side ports, actually... it's because they could give the intake port a much earlier opening without overlapping the exhaust. Exhaust closes at 3*BTDC, intake opens at 3*ATDC... as opposed to 32* that they used to open at. The side exhaust lowers the misfiring a lot too... which helps power and economy/emissions. From a question from the floor, the emissions characteristics are only about 30% greater than their piston engins.

The other thing is a newly designed side seal to prevent carbon fouling. To make a long story short, they're keystone shaped... wider at the housing surface and tapering down as they go farhter in. This means less carbon buildup in the slot, for some reason I didn't quite get.

I also asked afterwards about long-term reliability of the smaller apex seals. They said they changed the metallurgy to keep reliable... and smiled politely and apologized for not being able to say what alloy. Their response about getting back into racing was similar.

 

a rotary isn't geared for convenience, it's geared for necessity. sorry mr. output shaft arguer.

 

That is of the no consequence, the fact is it is geared. It would also be possible to gear the output shaft differently again while keeping the internal operation the same. I could then design the calculated capacity to be whatever I liked for the exact same engine.

 

then why does anyone bother trying to educate you when your argument consistently is 'i can do what i want to to make the displacement how i see fit'

now i know why the older owners stay away from these threads.

 

With respect, you have misunderstood what I meant. What I meant was the air inducted per 2 revs method is not valid because I can easily change the way I take the drive of the engine to get whatever figure I want, without changing the fundamental design of the engine. If I took the drive off the camshaft of a piston motor then it's capacity would double. If I took the drive off the rotation of the rotor it's capacity would change (I can't be bothered figuring out what it would change to at the mo). If I added a hidden gear to the output shaft of a piston motor its capacity would change. Well, its capacity wouldn't actually change, just the figure obtained using the "per 2 revs" method would.

The correct method is to measure the air inducted for each chamber/cylinder to complete a full 4 stroke cycle. On yer standard 4 stroke piston motor this gives the same figure. It also still gives the same figure for the piston motor with the drive taken off the cam or with the output shaft geared. And it gives 3.9 litres for the 13b.

Did you read this?

http://mikesdriveway.com/misc/rotor.doc

 

You are one of only 2 people I've know of to understand the 3.9litre overdrive motor and you are the only person I know of besides me who has actually come up with the concept. But I don't think you realise the full significance of this. Pretty much everything that applies to this geared up motor applies to the rotary. If the output shaft of the geared up motor is doing 9000rpm then the 'real' engine speed is 6000. The torque is actually 1.5 times higher than what you get at the output shaft. The expansion is over 270*, there are the same number of ignitions per second and at the same time. If you froze both motors at any point in time then the volumes of each chamber would correspond. The sum of the volumes in both motors is always the same at any point in time. Plus everything I mentioned in the article is the same, such as torque fluctuation graphs. The rotary really *is* this engine for the purposed of displacement.

 

Actually, NSU engineers originally used the formula which would of made the 13B a 3.9L engine. They only switched to the 1.3L formula to make the cars sell better. This was due to European taxes.

Thought that might be relevant...

 

Once and for all 13b's will "MOVE":
1.3L of air in one rotation of the e-shaft.

2.6L of air in two rotations of the e-shaft. Which is why it's compared to a 4 stroke piston engine.

3.9L of air in three rotations of the e-shaft.

End of debate!

 

Of course, the engineers got it right. At the start of the project the engineers would have rated the engine. At the end of the project the accounting and marketing departments would have rated it. Anyone care to guess which department would have got it right

BTW, do you have a reference to this? Did you read this in a book?

Cheers,
Michael

 

Yes.

It was one of these 3. I can't remember which one. I read them all at the same time about 2 months ago so I can't recall for sure. Sorry I can't be more clear. Regardless, they're all good books that I recommend.

The Wankel Rotary Engine: A History
John B. Hege





The Wankel Engine: The Story of the Revolutionary Rotary Engine
Nicholas Faith





The Wankel Rotary Engine: Introduction and Guide
Harris Edward Dark

 

Although I'm pretty sure it is in one of those books, I found it in an article I had saved.

"How big are Wankel engines?" by Karl Ludvigsen (2003).

When Max Bentele, a Curtiss-Wright enginner, firsxt visited Wanekl prime licensee NSU in mid 1958, he copied down a list of all the rotary engines that NSU had build and was planning. In each case, NSU had shown the displacement as three times that of a single chamber. The first experimental engines, which had 125cc chambers, were classified as 375cc units. Projected engines with 500cc chambers were described as 1.5 litre units in single-bank form and as 3.0 liter engines with two banks.

Bentele brought the NSU engineers up short with a cautionary comment. "Aren't you asking for trouble?" he asked. "We have no problem in the US with taxation on the basis of engine szie, but you do in Europe. Why do you mention three chambers when you could mention only one?" Whether or not Bentele's advice was influential, NSU did indeed go back to a single-chamber rating for all its Wankels.

The full article, although only 4 pages, is a good read. I still highly recommend the books I previously mentioned.

 

Interesting quote, pretty much exactly what I suspected happened. It's a bit like rating a 3 cylinder engine on the size of 1 cylinder. :-) Would you be able to email the article?

 

Shouldn't be a problem. PM me with your info and I'll see what I can do.

 

There's also a reference to an SAE paper that Wankel wrote that was solely devoted to the problem of classifying the displacement of rotaries. I'm trying to find it, no luck yet.

 

who says that all the numbers for swept volume of piston units is correct!! I have been asking this question for 40 yrs, ( WHO invented the DIGITS), what kind of nut case would do such a thing to the HUMAN race, SIMPLE his EGO wanted to keep track of his SLAVES, he could give less a crap about money, he wanted # on his slaves. NUFF said!! NOW thats POWER. its called mind control. the formulas are being broken everyday. THX for your interest, RON thats why rotarys dont JIVE.

 

ya gotta get off the stuff ...

 

Thanks for the article, I read it with great interest. I studied the topic of rotary capacity extensively at uni and on and off over the 14 years since. I've read everything I can find on this topic and rarely find an article that I would consider 100% accurate. Even articles by some of the supposed experts say things that I consider wrong. In some cases, such as Yamamoto and Wankel you can tell they know exactly what they are talking about but are trying to skirt the issue of capacity. Calling the 13B a 654cc x 2 is obviously avoiding the issue but I can't blame them, if someone was going to give me millions to develop my favourite toy i'd do the same thing in an instant. :-) Other authors such as Jan P Norby and Richard F. Ansdale make ludicrous statements which leave you scratching your head, eg

http://www.geocities.com/jeffguilfoi...lacement1.html

Anyway, the point I was getting to the long way round was the article by Karl Ludvigsen was the first article I've read that I've considered 100% accurate. Many other articles I've read have been technically correct but not what I would consider 100% accurate. Many of the points in Karl's article have been what I've been saying in newsgroups and forums for years. eg:

he stated you can't use the output shaft to base any measurements for capacity nor can you base any arguements on the rotation of the output shaft. For example you can't say the 13B is 2.6 litres because it inducts 2.6 litres of air in 2 revs. This is because a small change in the design of the engine, such as taking drive from the rotation of the rotor, would change that figure.

The output shaft spins 1.5 times faster than it otherwise would due to the 270 degree stroke. This is what causes the rotary to appear to rev higher than piston motors but in fact it is actually doing 1.5 times less internally than the output shaft.

This 1.5 times factor is more of an impediment than a feature, instead of allowing the rotary to rev higher it forces it to rev higher to compete with similar sized piston motors.

The graph of volume over shaft rotation for a 13B is very similar to that of a 3.9 litre 6 cylinder piston motor that has been geared up by a factor of 1.5 at the output shaft.

The diagrams comparing the 3 pistons at 120 degrees to the rotary is very similar to an animation I wrote in software.